As electronic devices become smaller, there is a continuing desire in the electronics industry to increase the circuit density in electronic components, e.g., integrated circuits, circuit boards, multichip modules, chip test devices, and the like without degrading electrical performance, e.g., crosstalk or capacitive coupling, known as RC delay, and also to increase the speed of signal propagation in these components. One method of accomplishing these goals is to reduce the dielectric constant of the interlayer insulating material used in the components that separate the signal carrier species. A method for reducing the dielectric constant of such interlayer insulating material is to incorporate within the insulating film very small, uniformly dispersed pores or voids. Since air and other gasses have the lowest dielectric constants, their incorporation significantly lowers the overall dielectric constant. Most materials are limited in the amount of air pockets they can contain and still maintain structural integrity.
A variety of organic and inorganic dielectric materials are known in the art as insulating films in the manufacture of electronic devices, particularly integrated circuits. Suitable inorganic dielectric materials include silicon dioxide and organo polysilicas. Suitable organic dielectric materials include thermosets such as polyimides, polyarylene ethers, polyarylenes, polycyanurates, polybenzazoles, benzocyclobutenes and the like.
Methods of providing porous dielectrics have focused on incorporating particles into the dielectric which are later removed using heat processes. In general, porous dielectric materials are prepared by first incorporating a removable particles into a B-staged dielectric material, disposing the B-staged dielectric material containing the removable particle onto a substrate, curing the B-staged dielectric material and then removing the particle to form pores in the dielectric material. For example, U.S. Pat. No. 5,895,263 (Carter et al.) discloses a process for forming an integrated circuit containing porous organo polysilica dielectric material. U.S. Pat. No. 6,093,636 (Carter et al.) discloses a process for forming an integrated circuit containing porous thermoset dielectric material. Gallagher in U.S. Pat. No 6,596,467B2 also describes the use of pore generating materials in dielectrics. In each of these patents, the amount of pores that can be created is limited due in part to the amount of heat needed to depolymerize the particles while maintaining the strength and integrity of the composition. Because there is a limit as to how much of the dielectric can contain pores, the value of the dielectric can not reach below about 2 without compromising the dielectric layer. Also, in the Carter patents, the process described requires the step of forming the porous dielectric material prior to any subsequent processing steps, while in the Gallagher patent the dielectric is fully or partially covered with metal or other materials hindering the removal of the by-products of the depolymerized particles. There is thus a need for processes for manufacturing electronic devices including porous dielectric materials that have dielectric constants below around 2.0 while maintaining the structure integrity of the material.